How A Blocking Diode Works & Testing A Diode With A Multimeter

Read the full blog post here: http://www.thediyworld.com/blog/?p=1610

I had a blocking diode fail on me a few days back. It was the diode between the wind turbine and my battery bank. This diode actually became a zero resistance two way conductor and drained my battery bank through the DC wind turbine.

A diode is like a one way valve. It allows electricity to flow in one direction but blocks it from flowing in the other direction.

When a diode fails it can sometime short right out and conduct electricity in both directions. This is what happened to mine.

There is a silver band on a diode. This is the negative side. The other end is the positive side. So if you want power to flow from your wind turbine like mine, for example, then you would have the positive wire form the wind turbine connected to the positive side of the diode. Then the negative side of the diode on the battery bank plus terminal.

You can test a diode with a multimeter set on Ohms scale. Using the meter on a medium Ohms setting simple connect the test leads to the diode. Either way, it is not important for this test.

In one direction you will measure some resistance. In the other direction the flow of electricity will be blocked and you will measure infinite resistance.

When a diode blows out like mine did, you will have energy being conducted in both directions. My blown diode actually shows zero resistance in both directions. This is quite surprising. It is no wonder my battery bank was drained through the wind turbine.

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